Subject: Re: [patch net] ipv6: do not create neighbor entries for local delivery

From: Marcelo Ricardo Leitner <[email-masked]>
Date: Thu, 08 Aug 2013 16:11:28 -0300

Em 08-08-2013 16:06, Hannes Frederic Sowa escreveu:
> On Thu, Aug 08, 2013 at 04:02:36PM -0300, Marcelo Ricardo Leitner wrote:
>> Em 08-08-2013 16:01, Hannes Frederic Sowa escreveu:
>>> On Thu, Aug 08, 2013 at 02:45:40PM -0400, Debabrata Banerjee wrote:
>>>> On Wed, Jan 30, 2013 at 3:26 AM, Jiri Pirko <[email-masked]> wrote:
>>>>> From: Marcelo Ricardo Leitner <[email-masked]>
>>>> I'm not sure this patch is doing the right thing. It seems to break
>>>> IPv6 loopback functionality, it is no longer equivalent to IPv4, as
>>>> stated above. It doesn't just stop neighbor creation but it stops
>>>> cached route creation. Seems like a scary change for a stable tree.
>>>> See below:
>>>>
>>>> $ ip -4 route show local
>>>> local 127.0.0.0/8 dev lo  proto kernel  scope host  src 127.0.0.1
>>>>
>>>> This local route enables us to use the whole loopback network, any
>>>> address inside 127.0.0.0/8 will work.
>>>>
>>>> $ ping -c1 127.0.0.9
>>>> PING 127.0.0.9 (127.0.0.9) 56(84) bytes of data.
>>>> 64 bytes from 127.0.0.9: icmp_seq=1 ttl=64 time=0.012 ms
>>>>
>>>> --- 127.0.0.9 ping statistics ---
>>>> 1 packets transmitted, 1 received, 0% packet loss, time 0ms
>>>> rtt min/avg/max/mdev = 0.012/0.012/0.012/0.000 ms
>>>>
>>>> This also used to work equivalently for IPv6 local loopback routes:
>>>>
>>>> $ ip -6 route add local 2001:::/64 dev lo
>>>> $ ping6 -c1 2001::9
>>>> PING 2001::9(2001::9) 56 data bytes
>>>> 64 bytes from 2001::9: icmp_seq=1 ttl=64 time=0.010 ms
>>>>
>>>> --- 2001::9 ping statistics ---
>>>> 1 packets transmitted, 1 received, 0% packet loss, time 0ms
>>>> rtt min/avg/max/mdev = 0.010/0.010/0.010/0.000 ms
>>>>
>>>> However with this patch, this is very broken:
>>>>
>>>> $ ip -6 route add local 2001::/64 dev lo
>>>> $ ping6 -c1 2001::9
>>>> PING 2001::9(2001::9) 56 data bytes
>>>> ping: sendmsg: Invalid argument
>>>>
>>>> --- 2001::9 ping statistics ---
>>>> 1 packets transmitted, 0 received, 100% packet loss, time 0ms
>>>
>>> Which kernel version are you using? Perhaps you miss another fix? It works
>>> for
>>> me. Also I cannot find this patch in net-next?
>>
>> It wasn't needed/applied as the route cache was removed.
>
> Do you mean the rt->n(eighbour) removal? There was no removal of a route cache
> in IPv6 land. The cache is merely in the routing table itself.

Yes, my bad, sorry. s/route/neighour/. It was discussed on this thread:
http://article.gmane.org/gmane.linux.network/255318

"Note also that YOSHIFUJI Hideaki's patches to remove the cached neighbour
entirely from ipv6 routes will have the same effect, so your patch won't
be needed."

Thanks,
Marcelo